Storage of hazardous materials

ABSTRACT

A nuclear material is encapsulated by treating the material with an encapsulant that includes a cementitious material and curing the cementitious material. The nuclear material includes uranium metal, Magnox fuel elements, and/or fuel element debris.

FIELD OF THE INVENTION

This invention relates to a method for the treatment and storage ofhazardous materials by encapsulation. More specifically, it is concernedwith the encapsulation in cementitious media of materials encountered inthe nuclear industry, and has specific application to uranium andso-called Magnox fuel elements.

BACKGROUND TO THE INVENTION

Encapsulation has proved to be an especially favoured method for thedisposal of certain hazardous materials; specifically it provides asuitable means for the conversion of these materials into a stable andsafe form, which allows for long-term storage and/or ultimate disposal.The technique can find particular application in the nuclear industry,where the highly toxic and radioactive nature of the materials involved,and the extended timescales over which the toxicity is maintained, arethe principal considerations when devising safe disposal methods.

In co-pending GB patent application No. 0130593.7, the present applicanthas disclosed the use of cementitious grouting materials for theencapsulation of fine particulate sized wastes and provided details of amethod for the encapsulation of fine particulate materials whichcomprises treating these materials with at least one microfine hydraulicinorganic filler.

The use of cement based injection grouting in the construction industryis well known from the prior art. Thus, EP-A-412913 teaches the use of aPortland Cement based grout in the consolidation of concrete structuresaffected by fine cracks, providing a cost-effective means of infillingboth superficial and deeper fissures and cavities in such structures,including such as buildings, bridges and dams. Similarly, ZA-A-9209810is concerned with a pumpable, spreadable grouting compositionincorporating a cementitious and/or pozzolanic or equivalent material,and its application in sealing fissures and cracks, back-filling,providing mass fills in civil and mining works, or lining tunnels.

Also disclosed in the prior art are hydraulic setting compositionscomprising particles of Portland Cement together with fine particles ofsilica fume containing amorphous silica, which are the subject ofEP-A-534385 and are used in the production of concrete, mortar or grouthaving improved fluidity, whilst GB-A-2187727 describes a rapid gelling,hydraulic cement composition which comprises an acrylic gelling agent, afine filler and Portland Cement, this composition being thixotropic andfinding particular application in the formation of bulk infills forunderground mining, and in the filling of voids and cavities inconstruction or civil engineering. A composition which also is useful ingeneral building and construction work, and as an insulating materialcomprises a particulate filler, cellulose fibres and a cementitiousbinder, and is disclosed in GB-A-2117753.

Whilst the majority of these compositions of the prior art have arequirement for the addition of water, EP-A-801124 is concerned with adry mixture, used for fine soil injection grout preparation, the mixturecomprising fillers which do not react with water, cement anddeflocculant; on addition of water, an agglomerate-free fine grout isformed, and this is easily injected into fine soil.

Thus, the use of such grouting materials in—primarily—civil engineeringis well known, and its use in treating fine particulate sized wastes inthe nuclear industry is the subject of the above co-pending application.However, whilst attempts have previously been made to encapsulate brokenMagnox fuel elements, the treatment of uranium metal and complete Magnoxfuel elements involved in nuclear processing has always been reliant onreprocessing techniques, many of which are well known to those skilledin such technology. Nevertheless, there has long been a need for analternative approach for dealing with such fuel materials, particularlyfor those cases where reprocessing is especially difficult orhazardous—or, on occasions, impossible.

The present inventors have now found that cured cementitious materialsmay advantageously be employed for the long term encapsulation ofuranium and Magnox fuel elements, as well as fuel element debris,thereby providing a product which remains stable and monolithic for manyhundreds of years. Hence, a treatment method is provided which affordsmuch greater efficiency, convenience and safety in handling, and has aconsequent beneficial effect both in terms of environmentalconsiderations and cost, thereby satisfying a long felt need in thenuclear industry wherein the waste management of materials is receivingever greater attention in the global drive to ensure ever higher safetystandards.

STATEMENTS OF INVENTION

Thus, according to the present invention there is provided a method forthe encapsulation of a nuclear material which comprises treating thematerial with an encapsulant which comprises a cementitious material andcuring said cementitious material.

Generally, the nuclear material comprises a nuclear fuel material suchas uranium metal or Magnox fuel elements or fuel element debris.Alternatively, it may comprise, for example, fast reactor fuel, metaloxide fuel or mixed oxide fuel.

The cementitious material may typically comprise, for example, PortlandCement or a similar commercially available product.

One or more additional inorganic fillers may optionally be added to thecementitious material; suitable fillers include blast furnace slag,pulverised fuel ash, hydrated lime, finely divided silica, limestoneflour and organic and inorganic fluidising agents.

The invention also provides a method for the storage of a nuclearmaterial which comprises encapsulation of the material in a curedcementitious material.

DESCRIPTION OF THE INVENTION

The method of the present invention is of particular value in thetreatment of nuclear fuel materials. Such materials may be treated bythis method in order to obtain a product which remains stable andmonolithic for many hundreds of years, thereby offering a safe andconvenient alternative means of handling other than nuclear fuelreprocessing.

There exists a considerable worldwide stock of such nuclear fuelmaterials which, whilst safely stored for the medium term, requires asuitable route for long term disposal. This accumulation of thismaterial provides powerful evidence of the absence of any suitablemethod of treatment. However, the present method now offers a safe andconvenient technique for their disposal which should provideconsiderable environmental benefits.

A particular example of the application of the method involves placingthe nuclear material in an appropriate container and adding a suitablecementitious material. Elements of the nuclear material may either bearrayed in the container or mixed haphazardly. The cementitious materialis then added and allowed to at least partially cure, and the containermay then be capped or, alternatively sent directly for storage or finaldisposal. The capping process involves placing a cap of cement on top ofthe mixture of nuclear material and cementitious material in thecontainer after this mixture has been allowed to partially cure; theprocedure has proved to be especially valuable in ensuring the safe longterm storage of the material, and it provides an additional benefit inthe reduction of secondary waste.

The container may comprise any container of an appropriate form andsize, for example a drum having a capacity in the region of 500 litres.In such a case, the amount of nuclear material which may safely bestored may be up to as many as 52 elements. Preferably, however, thenumber of elements would be of the order of 22.

Typically, the cementitious material is provided in the form of anaqueous composition with a water content preferably in the region of40-50% (w/w). Thus, the material may conveniently be pumped underpressure into the container.

1. A method for the encapsulation of a nuclear material, comprising:treating the nuclear material with an encapsulant which comprises acementitious material; and curing said cementitious material; whereinsaid nuclear material comprises uranium metal, Magnox fuel elements,and/or fuel element debris.
 2. (canceled)
 3. A method as claimed inclaim 1 wherein the cementitious material comprises Portland Cement. 4.A method as claimed in claim 1 wherein the cementitious material furthercomprises at least one inorganic filler, the at least one inorganicfiller comprising blast furnace slag, pulverised fuel ash, hydratedlime, finely divided silica, limestone flour and/or organic andinorganic fluidising agents.
 5. A method as claimed in claim 1 whereinthe cementitious material is provided in the form of an aqueouscomposition.
 6. A method as claimed in claim 5 wherein the water contentof the composition is about 40-50% (w/w).
 7. A method as claimed inclaim 1 further comprising: placing the nuclear material in a containerbefore treating the nuclear material and curing the cementitiousmaterial.
 8. A method as claimed in claim 7 wherein elements of thenuclear material are either arrayed in the container or mixedhaphazardly.
 9. A method as claimed in claim 7 further comprising:capping the container after the cementitious material has at leastpartially cured.
 10. A method as claimed in claim 7 wherein thecontainer comprises a drum having a capacity of about 500 litres.
 11. Amethod as claimed in claim 10 wherein an amount of nuclear materialstored in the container is up to about 52 elements.
 12. A method asclaimed in claim 11 wherein the number of elements is about
 22. 13. Amethod of storing a nuclear material comprising: encapsulating thenuclear material in a cured cementitious material, wherein said nuclearmaterial comprises uranium metal, Magnox fuel elements, and/or fuelelement debris.